Under reaming open hole sections during drilling operations using hydraulic and/or mechanically activated downhole tools has become accepted practice in the oil and gas industry. The under reamed hole section improves equivalent circulating densities during drilling, aids the subsequent installation of casing strings due to increased clearance between casing and the open hole and, conversely, makes possible tighter clearance casing programs which may be desirable during the construction of deeper wells. It has now become common practice to under ream sections of well bore using multi-cycle hydraulic under reamers.
It is known to control a multi-cycle downhole tool using an indexing mechanism which is configured to repeatedly toggle the operational state of the downhole tool between a de-activated state in which the downhole tool is in a radially retracted configuration and an activated state in which the downhole tool is in a radially extended configuration. In such methods, actuation of the indexing mechanism is often achieved by circulating a ball to depth. However, such known indexing mechanisms may not permit control of multiple downhole tools on the same drill string.